Highly Efficient Oxidation of Amines to Aldehydes with Flow-based Biocatalysis

Article abstract of DOI:10.1002/cctc.201701147

A new mild and efficient process for the aqueous preparation of aldehydes, which are employed as flavour and fragrance components in food, beverage, cosmetics, as well as in pharmaceuticals, was developed using a continuous-flow approach based on an immobilised pure transaminase-packed bed reactor. HEWT, an ω-transaminase from the haloadapted bacterium Halomonas elongata, has been selected for its excellent stability and substrate scope. Sixteen different amines were rapidly (3–15 min) oxidised to the corresponding aldehydes (90 to 99 %) with only 1 to 5 equivalents of sodium pyruvate. The process was fully automated, allowing for the in-line recovery of the pure aldehydes (chemical purity >99 % and isolated yields above 80 %), without any further work-up procedure.

Full text of DOI:10.1002/cctc.201701147

DOI: 10.1002/cctc.201701147
Full Papers
Highly Efficient Oxidation of Amines to Aldehydes with
Flow-based Biocatalysis
[
a, b]
[c]
[c]
[d]
Martina L. Contente,
Francesca Paradisi*
Federica Dall’Oglio, Lucia Tamborini,* Francesco Molinari, and
[
a, b]
A new mild and efficient process for the aqueous preparation
of aldehydes, which are employed as flavour and fragrance
components in food, beverage, cosmetics, as well as in phar-
maceuticals, was developed using a continuous-flow approach
based on an immobilised pure transaminase-packed bed reac-
tor. HEWT, an w-transaminase from the haloadapted bacterium
Halomonas elongata, has been selected for its excellent stabili-
ty and substrate scope. Sixteen different amines were rapidly
(3–15 min) oxidised to the corresponding aldehydes (90 to
99%) with only 1 to 5 equivalents of sodium pyruvate. The
process was fully automated, allowing for the in-line recovery
of the pure aldehydes (chemical purity >99% and isolated
yields above 80%), without any further work-up procedure.
Introduction
[
5]
Aromatic aldehydes are important intermediates in a number
of synthetic processes and have a prominent role as flavour
dant. Aromatic aldehydes can also be enzymatically prepared
using other approaches, such as oxidation of primary alco-
[1]
[6]
[7]
and fragrance components. Among other synthetic methods,
hols and reduction of carboxylic acids.
they can be obtained from the corresponding primary aromat-
ic amines, which are readily available substrates. Methods for
the oxidation of amines to carbonyl compounds have received
significant attention, but these approaches are frequently
poorly sustainable, because they produce waste and by-prod-
ucts that are difficult to recycle, require drastic reaction condi-
In this context, we developed an efficient bio-preparation of
nature-identical flavours and fragrances exploiting the immobi-
lised amine transaminase from the moderate halophilic bacteri-
[8]
um Halomonas elongata (HEWT), which is able to tolerate a
range of temperature, pH, salts and co-solvents in a continu-
ous flow reactor. The combination of biocatalysis and flow re-
actor technology can be considered as an enabling methodol-
ogy intrinsically compatible with the principles of green
[
1a,2]
tions, and often proceed with poor selectivity.
Biocatalytic processes are interesting alternatives for amine
oxidations under mild and benign conditions. For example,
copper amine oxidases (CAOs) have been used to catalyse the
[9]
chemistry. Flow-based biocatalysis was recently applied for
[
10]
peptide condensation,
hydrolysis and formation of esters
[11]
[12]
oxidation of primary amines to aldehydes (while O is simulta-
and sugars, stereoselective carbonyl reduction, formation
2
[
3]
[13]
[14]
neously reduced to H O ). Vanillin has been prepared by oxi-
of CꢀC bonds, production of nucleosides, monosacchar-
2
2
[15] [16]
dation of vanillylamine using an amine oxidase (AO) from As-
ides, and oligosaccharides, and interconversion of carbon-
[
4]
[17]
pergillus niger. Recently, selective oxidation of amines to alde-
hydes has been obtained using a laccase with TEMPO (2,2,6,6-
tetramethylpiperidine N-oxide) as mediator and O2 as oxi-
yls and amines using transaminases.
We recently reported on the application of HEWT in flow for
[18]
the biosynthesis of amines and we describe here an eco-
friendly and scalable process that enhances the oxidising capa-
bility of this covalently immobilised enzyme for the production
of aldehydes. The products are aromatic aldehydes used as fla-
vours and fragrances in food, beverage, cosmetics and phar-
maceuticals. They have been obtained in excellent yields, with
unprecedented reaction times if compared with traditional
batch methods. The use of pyruvate as amino acceptor is ex-
tremely favourable and by-product which it generates, the nat-
ural amino acid l-alanine, is completely benign and can be
easily recovered. Furthermore, this approach circumvents po-
tential issues often encountered with whole-cell biotransforma-
tions, such as generation of debris, swelling and permeability.
[a] Dr. M. L. Contente, Prof. F. Paradisi
School of Chemistry
University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
E-mail: Francesca.Paradisi@nottingham.ac.uk
[b] Dr. M. L. Contente, Prof. F. Paradisi
UCD School of Chemistry
University College Dublin
Belfield, Dublin 4 (Ireland)
[
c] F. Dall’Oglio, Dr. L. Tamborini
Department of Pharmaceutical Sciences, DISFARM
University of Milan
Via Mangiagalli 25, 20133 Milan (Italy)
E-mail: lucia.tamborini@unimi.it
[d] Prof. F. Molinari
Department of Food, Environmental and Nutritional Science, DeFENS
University of Milan
via Mangiagalli 25, 20133 Milan (Italy)
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Results and Discussion
Pure HEWT (imm-HEWT) was immobilised on an epoxy-resin as
[
18]
reported by Planchestainer et al. and the supported biocata-
ꢀ
1
lyst (5 mggramresin ) was then used in a packed-bed flow reac-
tor. The system was firstly tuned by optimising the preparation
of benzaldehyde starting from the corresponding benzylamine
(Scheme 1).
Scheme 2. Solution A: 20 mm solution of amines (entries 1–8) in phosphate
buffer (50 mm, pH 8.0) with 10% DMSO. Solution B: 20 mm, solution of pyru-
vate containing 0.1 mm PLP. T=378C, P=atm.
the packing material, despite various and extensive washing
steps.
A liquid-liquid-phase reaction system was therefore set up,
in which toluene flowed into the system upstream of the
packed column (Scheme 3). On acidification, downstream of
the process, the products 2i and 2j were extracted in-line and
recovered by membrane separation as pure compounds. Re-
markably, the presence of toluene had no effect on the catalyt-
ic efficiency of the immobilised enzyme which was extensively
used over several weeks.
Scheme 1. Solution A: 20 mm solution of benzylamine in phosphate buffer
50 mm, pH 8.0) containing 10% DMSO. Solution B: 20 mm solution of pyru-
vate containing 0.1 mm PLP. T=378C, P=atm.
(
To maximise the solubility of the amine, 10% of DMSO was
used as co-solvent in the phosphate buffer (50 mm, pH 8.0).
The reaction was performed under optimised conditions at
378C and atmospheric pressure with just one equivalent of
pyruvate, as the equilibrium for this reaction is extremely fa-
vourable; complete substrate oxidation (molar conversion
>
99%) was obtained with only 3 minutes of residence time
ꢀ
1
(flow rate 0.3 mLmin ).
Notably, the use of the same immobilised enzyme in batch
gave a full oxidation in about 2 hours.
The optimised conditions were applied to the bioconversion
of different benzylamines into the corresponding flavour alde-
hydes (Table 1).
Scheme 3. Solution A: 20 mm solution of amines (entries 9, 10 Table 1 or
14–16 Table 2) in phosphate buffer (50 mm, pH 8.0). Solution B: 20 mm,
4
4
0 mm or 100 mm solution of pyruvate containing 0.1 mm PLP. T=37 or
58C, P=atm. Toluene is added at the same flow rate to form a 50:50 bipha-
Specific reaction rates in the batch and continuous-flow sys-
tems were calculated using the equations reported in the Ex-
perimental Section; the time taken (conversion rate) for the re-
action to reach maximum conversion, whether in batch or con-
tinuous-flow, was calculated and normalised to the amount of
sic stream.
A second set of amines (1k–1p) was investigated using the
same methodologies (either in a monophasic environment or
the biphasic one) to prove the versatility of the system with
different aromatic substrates. (Table 2).
[
11a]
catalyst used for both set-ups.
Benzylamine-derivatives (entries 1–8) were oxidised into the
corresponding aroma-compounds with high molar conversion;
in all cases, a greater than 4-fold rate increase was observed if
reactions were conducted under flow conditions, as conver-
sions ꢁ 90% were reached within a residence time between 3
The batch oxidation of the tested (aryl)alkyl amines with
methyl/ethyl side chain (entries 11–14) allowed for the prepara-
tion of flavour aldehydes 2k (hyacinth note), 2j (floral note),
2m (floral note), and 2n (violet note) with excellent conversion
(>99%), although the reactions required several hours to go
to completion. In line with our observations for the benzyla-
mine derivatives, the same molar conversion was obtained
within 3 to 15 minutes of residence time in flow, thus strongly
increasing the overall productivity. In particular, piperonyla-
mine (1n) was successfully converted into the corresponding
aldehyde (piperonal 2n, the violet fragrance, also known as he-
liotropin) in only 15 minutes (14-fold faster reaction rate) with
>99% conversion at 458C, demonstrating the good stability
and adaptability of this enzyme also at higher temperatures.
Both (S) and (R)-2-phenyl-1-propylamine (1l and 1m, respec-
ꢀ
1
ꢀ1
and 10 minutes (flow rate 0.3 mLmin and 0.1 mLmin , re-
spectively), at 378C and atmospheric pressure.
The process was implemented with the addition of an in-
line acidification step followed by extraction with EtOAc. The
two phases were continuously separated using a Zaiput liquid/
liquid separator and the desired aldehydes were recovered in
the organic phase, significantly accelerating the overall work-
up, as no further purification is required (Scheme 2).
This protocol was successfully applied to substrates 1a–1h.
Aldehydes obtained from substrates 1i and 1j (entries 9 and
10) proved initially difficult to recover as they were retained by
&
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[
a]
Table 1. Preparation of aromatic benzaldehyde derivatives from the corresponding amines.
[
b]
[b]
Entry
Substrate
Reaction time
min]
M. c.
[%]
Conv. Rate
[mmolmin
Residence time
[min]
M. c.
[%]
Conv. Rate
ꢀ
1
ꢀ1
ꢀ1 ꢀ1
[
g
]
[mmolmin g ]
1
2
3
4
5
6
7
120
120
120
120
120
300
300
>99
>99
>99
>99
>99
>99
>99
0.83
3
>99
>99
>99
>99
>99
90
4.24
0.83
0.83
0.83
0.33
0.33
0.33
3
3
4.24
4.24
4.24
1.41
1.29
1.29
3
10
10
10
90
8
9
120
300
>99
>99
0.83
0.33
3
95
4.07
[
c]
[c]
10
>99
1.41
[
c]
[c]
1
0
300
>99
0.33
10
>99
1.41
[a] Reactions were performed in the presence of 10 mM substrates and pyruvate, 0.1 mM PLP, 10% DMSO was used as co-solvent at 378C. Isolated yields
are reported in the Experimental Section. [b] Conversion rates are normalised to the amount of enzyme used in the reaction and calculated as reported in
Ref. [11a]. [c] Liquid-liquid-phase flow stream (see procedure summarised in Scheme 3), in this case DMSO was not added to the buffer.
tively) were suitable substrates for HEWT. The enzyme equally
converted both enantiomers and did not show any stereopre-
ference for this particular molecule (entries 12 and 13).
conversion after 24 hours (50 and 52%), without any signifi-
cant increase over a longer incubation time, likely owing to an
unfavourable equilibrium. Under flow conditions, with one
equivalent of pyruvate, the conversions achieved were 50%
and 25% respectively, despite increasing the residence time to
30 min. To displace the equilibrium, the concentration of pyru-
vate was increased to 2 and 5 equivalents with respect to the
aldehydes 1o and 1p, yielding 95% of cinnamaldehyde and
However, the oxidation of cinnamylamine (1o, entry 15) to
cinnamaldehyde (2o, cinnamon aroma) and hydrocinnamyla-
mine (1p, entry 16) to hydrocinnamaldehyde (2p, honey
aroma), appeared more challenging. The batch reaction with
an equimolar concentration of amino donor resulted in poor
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[
a]
Table 2. Preparation of aryl-alkyl aldehydes from the corresponding amines.
[
b]
[b]
Entry
Substrate
Reaction time
M.c.
[%]
Conv. Rate
[mmolmin
Residence time
[min]
M.c.
[%]
Conv. Rate
ꢀ
1
ꢀ1
ꢀ1 ꢀ1
[min]
g
]
[mmolmin g ]
1
1
120
>99
>99
0.83
3
3
>99
>99
4.24
1
1
2
3
180
180
0.55
0.55
4.24
4.24
>99
3
>99
[
[
[
c,d]
[c,d]
14
15
16
1440
1440
300
>99
50
0.07
0.04
0.04
15
15
15
>99
>99
90
0.95
c,d,e]
c,d,f]
[c,d,e,g]
1.02
[c,d,f,g]
24
0.86
[a] Reactions were performed in the presence of 10 mM substrates and pyruvate, 0.1 mM PLP, 10% DMSO was used as co-solvent at 378C. Isolated yields
are reported in the Experimental Section. [b] Conversion rates are normalised to the amount of enzyme used in the reaction and calculated as reported in
Ref. [11a]. [c] Liquid-liquid-phase flow stream (see procedure summarised in Scheme 3), in this case DMSO was not added to the buffer. [d] Reactions per-
formed at 458C. [e] 20 mm Pyruvate. [f] 50 mm pyruvate. [g] Calculated at a similar degree of conversion of the batch reaction.
[
19]
9
0% of the saturated aldehyde with 15 minutes of residence
(bio)catalyst and the enhanced heat and mass transfer, the
combination between biocatalysis and flow chemistry reactors
not only leads to significant reductions of reaction times and
increased productivity, but it can be also considered a sustain-
able technology for the production of aldehydes commonly
used in food, cosmetic, and pharmaceutical industry.
time at 458C. This result underlines the fact that process con-
trol strategies (in our case, the optimisation of stoichiometric
ratio of the substrates) help to maximise the productivity of
HEWT by accelerating the reaction, while shifting the equilibri-
um to the product’s side.
Conclusions
Experimental Section
A new biocatalytic method for the synthesis of aldehydes with
extensive applications as components of flavours and fragran-
ces was developed. This is the first example of a transaminase
exploited in a flow chemistry reactor under highly favourable
oxidising conditions for the preparation of aromatic aldehydes,
showing excellent adaptability and stability during the process-
es. The use of a flow-based approach allowed for dramatic ac-
celerations of the reactions, with isolated yields above 80%
and very short residence times (3–15 min) of the substrates.
This system required, in the majority of cases, only one equiva-
lent of pyruvate as the amino acceptor, which leads to the for-
mation of l-alanine as by-product. A successful implementa-
tion was achieved with an in-line extraction step, which per-
mitted the recovery of the desired pure aldehydes in the or-
ganic stream and l-alanine in the aqueous one, with an ex-
tremely simplified work-up procedure and almost no
manipulation. As a result of the high local concentration of the
Expression, purification, and immobilisation of HEWT in E.
coli
Protein expression and purification was performed following previ-
[8]
ously reported protocols in Cerioli et al.; immobilisation was con-
ducted according to the procedure reported by Planchestainer
[18]
et al.
Batch reactions with immobilised HEWT
Batch reactions using the imm-HEWT were performed in 1.5 mL
micro centrifuge tubes; 500 mL reaction mixture in 50 mm phos-
phate buffer pH 8.0, containing 10 mm pyruvate, 10 mm amino
donor substrate, 0.1 mm PLP, and 50 mg of imm-HEWT (5 mgg )
was left under gentile shaking at 378C. 10 mL aliquots were
quenched with trifluoroacetic acid (TFA) 0.2% every hour and then
analysed by HPLC equipped with a Supelcosil LC-18-T column
(250 mmꢁ4.6 mm, 5 mm particle size; Supelco, Sigma–Aldrich, Ger-
ꢀ1
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many). The compounds were detected using an UV detector at
10 nm, 250 nm or 280 nm after an isocratic run with 25% acetoni-
trile/75% water with TFA 0.1% v/v at 258C with a flow rate of
Comparison of the rates of the same reaction in a batch or flow-
mode was made at similar degrees of conversion.
2
ꢀ1
1
mLmin . The retention times in minutes are: benzylamine
(
4.1 min), benzaldehyde (9.4 min), p-methylbenzylamine (5.2 min),
Flow reactions in liquid-liquid-phase systems with immobi-
lised HEWT
p-tolualdehyde (16.4 min), p-methoxybenzylamine (4.4 min), p-ani-
saldehyde (10.3 min), p-ethylbenzylamine (5.0 min), p-ethylbenzal-
dehyde (16.5 min), p-hydroxybenzylamine (3.8 min), p-hydroxyben-
zaldehyde (10.5 min), p-isopropylbenzylamine (10.0 min), cuminal-
dehyde (35.0 min), 2-(aminomethyl)-phenol (3.7 min), salicylalde-
hyde (10.3 min), vanillylamine (3.7 min), vanillin (5.7 min), veratryla-
mine (4.1 min), veratraldehyde (8.0 min), 4-(aminomethyl)-2,6-
dimethoxyphenol (3.5 min), syringaldehyde (5.4 min), 2-phenethyla-
mine (3.9 min), phenylacetaldehyde (9.8 min), (R)-2-phenyl-1-pro-
pylamine (4.3 min), (S)-2-phenyl-1-propylamine (4.3 min), 2-phenyl-
propanaldehyde (10.9 min), piperonylamine (4.2 min), piperonal
20, 40 or 100 mm pyruvate in phosphate buffer (50 mm, pH 8.0)
containing 0.1 mm PLP, and 20 mm amino donor solutions were
prepared. The two solutions were mixed in a T-piece. A second
junction for additional supplement of toluene at the same flow
rate was installed before the packed enzyme column. The resulting
segmented flow stream was directed to the imm-HEWT. The flow
rate was varied and optimised. After an in-line acidification step, as
previously reported, the exiting flow stream was separated by a
Zaiput liquid/liquid separator. The organic and aqueous phases
were analysed by HPLC, exploiting a calibration curve (see condi-
tions above), and the toluene containing the desired product was
evaporated to yield the aldehydes.
(
9.9 min), cinnamylamine (6.6 min), cinnamaldehyde (15.6 min), hy-
drocinnamylamine (5.1 min), hydrocinnamaldehyde (13.6 min), con-
firmed by comparison with commercially available compounds.
Characterisation of the products
Flow reactions with immobilised HEWT
1
The purity of aldehydes was assessed by HPLC and H NMR.
Continuous flow biotransformations were performed using a R2+
1
H NMR spectra were recorded with
300 MHz) spectrometer. Chemical shifts (d) are expressed in ppm,
and coupling constants (J) are expressed in Hz.
a Varian Mercury 300
/R4 Vapourtec flow reactor equipped with an Omnifit glass column
(
(
(
0.3421 mm i.d ꢁ100 mm length) filled with 0.7 g of imm-HEWT
5 mgg ). A 20 mm sodium pyruvate in phosphate buffer (50 mm,
ꢀ1
pH 8.0) containing 0.1 mm pyridoxal phosphate, and 20 mm amino
donor solution with 10% of DMSO were prepared. The two solu-
tions were mixed in a T-piece and the resulting flow stream was di-
rected into the column packed with the biocatalyst (packed bed
reactor volume: 1.0 mL). The flow rate was varied and optimised.
An in-line acidification was performed by using an inlet of 1n HCl
1
Benzaldehyde (2a): colourless oil; yield 95%; H NMR (CDCl ) d=
1
3
0.00 (s, 1H), 8.15–8.12 (m, 2H), 7.67–7.51 ppm (m, 3H).
1
p-Tolualdehyde (2b): yellow oil; yield 96%; H NMR (CDCl ) d=
3
9
.95 (s, 1H), 7.74 (d, J=7.5 Hz, 2H), 7.32 (d, J=7.5 Hz, 2H),
2
.40 ppm (s, 3H).
ꢀ
1
aqueous solution (flow rate: 0.1 mLmin ) that was mixed to the
exiting reaction flow stream using a T-junction. The resulting aque-
ous phase was extracted in-line using a stream of EtOAc (flow rate:
1
p-Anisaldehyde (2c): colourless oil; yield 94%; H NMR (CDCl ) d=
3
9
.85 (s, 1H), 7.80 (d, J=8.0 Hz, 2H), 6.96 (d, J=8.0 Hz, 2H),
ꢀ1
0
.2 mLmin ) and a Zaiput liquid/liquid separator. Both the organic
3
.90 ppm (s, 3H).
and aqueous phase were analysed by HPLC using the above re-
ported conditions. The amount of substrate and product was eval-
uated by exploiting a previously prepared calibration curve. For
the optimisation procedure, the reactions have been performed by
injecting 250 mL of each starting solutions (volume of EtOAc used
for the in-line extraction: 1 mL). To isolate the product, 10 mL of
each starting solution has been used (volume of EtOAc used for
the in-line extraction: 40 mL). The organic phase, containing the al-
dehyde, was evaporated to yield the desired product.
1
p-Ethyl benzaldehyde (2d): yellow oil; yield 94%; H NMR (CDCl )
3
d=9.98 (s, 1H), 7.81 (d, J=8.1 Hz, 2H), 7.36 (d, J=8.1 Hz, 2H), 2.74
(q, J=7.5 Hz, 2H), 1.27 ppm (t, J=7.5 Hz, 3H).
1
p-Hydroxybenzaldehyde (2e): yellow solid; yield 92%; H NMR
CDCl ): d=9.61 (s, 1H), 7.60 (d, J=8.3 Hz, 2H), 6.73 ppm (d, J=
(
3
8
.3 Hz, 2H).
1
Specific reaction rates in batch and continuous-flow systems were
calculated using Equations 1 and 2:
Cuminaldehyde (2 f): colourless oil; yield 84%; H NMR (CDCl
) d=
3
9.98 (s, 1H), 7.84 (d, J=8.4 Hz, 2H), 7.40 (d, J=8.4 Hz, 2H), 3.00
(septet, J=6.9 Hz, 1H), 1.30 ppm (d, J=6.9 Hz, 6H).
hP
rbatch
¼
ðmmol= min gÞ
ð1Þ
1
t ꢂ mB
Salicylaldehyde (2g): yellow oil; yield 82%; H NMR (CDCl ) d=
3
11.00 (bs, 1H, OH), 9.85 (s, 1H), 7.46–7.54 (m, 2H), 6.94–7.00 ppm
(m, 2H).
where [n ] is the amount of product (expressed in mmol), t is the
p
reaction time (expressed in min), and m [g] is the amount of bio-
catalyst employed.
B
1
Vanillin (2h): white solid; yield 90%; H NMR (CDCl ) d=9.78 (s,
3
1
3
H), 7.37–7.40 (m, 2H), 7.02 (d, J=8.5 Hz, 1H), 6.72 (bs, 1H, OH),
.90 ppm (s, 3H).
½
Pꢃ ꢂ f
rflow
¼
ðmmol= min gÞ
ð2Þ
m
B
1
Veratrylaldehyde (2i): yellow solid; yield 96%; H NMR (CDCl ) d=
3
9
.85 (s, 1H), 6.70–7.65 (m, 3H), 3.98 (s, 3H), 3.95 ppm (s, 3H).
where [P] is the product concentration flowing out of the reactor
ꢀ
1
ꢀ1
1
(
expressed in mmolmL ), f is the flow rate (expressed in mLmin ),
Syringaldehyde (2j): yellow solid; yield 94%; H NMR (CDCl ) d=
3
and m [g] is the amount of biocatalyst loaded in the column.
9.83 (s, 1H), 7.15 (s, 2H), 6.10 (s, 1H), 3.98 ppm (s, 6H).
B
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c) E. I. Solomon, D. E. Heppner, E. M. Johnston, J. W. Ginsbach, J. Cirera,
M. Qayyum, M. T. Kieber-Emmons, C. H. Kjaergaard, R. G. Hadt, L. Tian,
Chem. Rev. 2014, 114, 3659–3853.
4] A. Yoshida, Y. Takenaka, H. Tamaki, I. Frꢃbort, O. Adachi, H. Kumagai, J.
Ferment. Bioeng. 1997, 84, 603–605.
1
Phenylacetaldehyde (2k): pale yellow oil; yield 97%; H NMR
CDCl ) d=9.70 (t, J=2.0 Hz, 1H), 7.30–7.10 (m, 5H), 3.56 ppm (d,
J=2.0 Hz, 2H).
(
3
[
[
5] P. Galletti, F. Funiciello, R. Soldati, D. Giacomini, Adv. Synth. Catal. 2015,
2
-Phenylpropanaldehyde (2l/2m): colourless oil; yield 90%;
H NMR (CDCl ) d=9.62 (s, 1H), 7.30–7.40 (m, 2H), 7.20–7.28 (m,
3
57, 1840–1848.
1
3
[6] a) F. Molinari, Curr. Org. Chem. 2006, 10, 1247–1263; b) D. Romano, R.
Villa, F. Molinari, ChemCatChem 2012, 4, 739–749; c) P. Zambelli, A.
Pinto, D. Romano, E. Crotti, P. Conti, L. Tamborini, R. Villa, F. Molinari,
Green Chem. 2012, 14, 2158–2161; d) A. Dꢄaz-Rodrꢄguez, L. Martꢄnez-
Montero, I. Lavandera, V. Gotor, V. Gotor-Fernꢅndez, Adv. Synth. Catal.
3
H), 3.60 (q, J=7.0, 1H), 1.45 ppm (d, J=7.0, 3H).
1
Piperonal (2n): white solid; yield 87%; H NMR (CDCl ) d=9.80 (s,
H), 7.40 (dd, J=7.9, 1.6 Hz, 1H), 7.32 (d, J=1.6 Hz, 1H), 6.92 (d,
3
1
2
014, 356, 2321–2329; e) R. A. Sheldon, Catal. Today 2015, 247, 4–13;
J=7.9 Hz, 1H), 6.07 ppm (s, 2H).
f) Y.-G. Zheng, H.-H. Yin, D.-F. Yu, X. Chen, X.-L. Tang, X.-J. Zhang, Y.-P.
1
Xue, Y.-J. Wang, Z.-Q. Liu, Appl. Microbiol. Biotechnol. 2017, 101, 987–
Trans-Cinnamaldehyde (2o): yellow oil; yield 89% H NMR (CDCl )
3
1001.
d=9.70 (d, J=7.7 Hz 1H), 7.55 (dd, J=5.2, 2.0 Hz, 2H), 7.50 (d, J=
5.9 Hz, 1H), 7.42–7.46 (m, 3H), 6.73 ppm (dd, J=15.9, 7.7 Hz, 1H).
[
7] a) M.-K. Akhtar, N. J. Turner, R. Patrik, P. R. Jones, Proc. Natl. Acad. Sci.
USA 2013, 110, 87–92; b) A. M. Kunjapur, Y. Tarasova, K. L. J. Prather, J.
Am. Chem. Soc. 2014, 136, 11644–11654; c) W. Finnigan, A. Thomas, H.
Cromar, B. Gough, R. Snajdrova, J. P. Adams, J. A. Littlechild, N. J.
Harmer, ChemCatChem 2017, 9, 1005–1017.
1
1
Hydrocinnamaldehyde (2p): pale yellow oil: yield 86% H NMR
CDCl ) d=9.76 (s, 1H), 7.35 (q, J=7.4 Hz, 2H), 7.25–7.30 (m, 3H),
3
(
[
8] L. Cerioli, M. Planchestainer, J. Cassidy, D. Tessaro, F. Paradisi, J. Mol.
Catal. B 2015, 120, 141–150.
3
.00 (t, J=15.1 Hz, 2H), 2.82–2.85 ppm (m, 2H).
[
9] a) S. V. Ley, Chem. Rec. 2012, 12, 378–390; b) J. M. Bolivar, J. Wiesbauer,
B. Nidetzky, Trends Biotechnol. 2011, 29, 333–342.
Acknowledgements
[
10] P. Falus, L. Cerioli, G. Bajnoczi, Z. Boros, D. Weiser, J. Nagy, D. Tessaro, S.
Servi, L. Poppe, Adv. Synth. Catal. 2016, 358, 1608–1617.
The authors wish to thank UK Biotechnology and Biological Sci-
ences Research Council (BBSRC; BB/P002536/1) for financial sup-
port (F.P., M.L.C), Science Foundation Ireland for initial funding
through Synthesis and Solid State Pharmaceutical Centre code
[
11] a) C. Csajꢅgi, G. Szatzker, E. R. Toke, L. ꢆrge, F. Darvasa, L. Poppe, Tetra-
hedron: Asymmetry 2008, 19, 237–246; b) I. I. Junior, M. C. Flores, F. K.
Sutili, S. G. F. Leite, L. S. D. M. Miranda, I. C. R. Leal, R. O. M. A. de Souza,
Org. Process Res. Dev. 2012, 16, 1098–1101; c) L. Tamborini, D. Romano,
A. Pinto, A. Bertolani, F. Molinari, P. Conti, J. Mol. Catal. B 2012, 84, 78–
12/RC/2275 (reagents and support, F.P).
82; d) L. Tamborini, D. Romano, A. Pinto, M. Contente, M. C. Iannuzzi, P.
Conti, F. Molinari, Tetrahedron Lett. 2013, 54, 6090–6093; e) I. Itabaiana,
L. S. de Miranda, R. O. M. A. de Souza, J. Mol. Catal. B 2013, 85–86, 1–9;
f) S. S. Wang, Z. J. Li, S. Sheng, F. A. Wu, J. Wang, J. Chem. Technol. Bio-
technol. 2016, 91, 555–562; g) F. Carvalho, M. P. C. Marques, P. Fer-
nandes, Catalysts 2017, 7, 42–60.
Conflict of interest
The authors declare no conflict of interest.
[
12] F. Dall’Oglio, M. L. Contente, P. Conti, F. Molinari, D. Monfredi, A. Pinto,
D. Romano, D. Ubiali, L. Tamborini, I. Serra, Catal. Commun. 2017, 93,
2
9–32.
Keywords: Aldehydes · Amine oxidation · Biocatalysis · Flow
reactor · Transaminase
[
[
[
[
13] J. Lawrence, B. O’Sullivan, G. J. Lye, R. Wohlgemuth, N. Szita, J. Mol.
Catal. B 2013, 95, 111–117.
14] E. Calleri, G. Cattaneo, M. Rabuffetti, I. Serra, T. Bavaro, G. Massolini, G.
Speranza, D. Ubiali, Adv. Synth. Catal. 2015, 357, 2520–2528.
15] L. Babich, A. F. Hartog, L. J. C. van Hemert, F. P. J. T. Rutjes, R. Wever,
ChemSusChem 2012, 5, 2348–2353.
16] P. Zambelli, L. Tamborini, S. Cazzamalli, A. Pinto, S. Arioli, S. Balzaretti,
F. J. Plou, L. Fernandez-Arrojo, F. Molinari, P. Conti, D. Romano, Food
Chem. 2016, 190, 607–613.
[
1] a) W. Kantlehner, Eur. J. Org. Chem. 2003, 2530–2546; b) “Preparation of
Aldehydes”: M. B. Smith in Compendium of Organic Synthetic Methods,
Vol. 13, Wiley-VCH, Weinheim, 2014, pp. 75–88.
[
2] a) T. F. Buckley, H. Rapoport, J. Am. Chem. Soc. 1982, 104, 4446–4450;
b) Y. Hu, H. Hu, Synth. Commun. 1992, 22, 1491–1496; c) K. Orito, T. Ha-
takeyama, M. Takeo, S. Uchiito, M. Tokuda, H. Suginome, Tetrahedron
1
1
998, 54, 8403–8410; d) N. A. Noureldin, J. W. Bellegarde, Synthesis
999, 939–942; e) J. Matsuo, A. Kawana, Y. Fukuda, T. Mukaiyama,
[
17] a) L. H. Andrade, W. Kroutil, T. F. Jamison, Org. Lett. 2014, 16, 6092–
6095; b) M. Bajic, I. Plazl, R. Stloukal, P. Znidarsic-Plazl, Process Biochem.
Chem. Lett. 2001, 30, 712–713; f) S. Sharma, N. Barooah, J. B. Baruah, J.
Mol. Catal. A 2005, 229, 171–176; g) H. Hamamoto, Y. Suzuki, H. Takaha-
shi, S. Ikegami, Tetrahedron Lett. 2007, 48, 4239–4242; h) D. A. Knowles,
C. J. Mathews, N. C. O. Tomkinson, Synlett 2008, 2769–2772; i) L. Liu, S.
Zhang, X. Fu, C. H. Yan, Chem. Commun. 2011, 47, 10148–10150; j) S.
Desjardins, G. Jacquemot, S. Canesi, Synlett 2012, 23, 1497–1500;
k) M. T. Schꢂmperli, C. Hammond, I. Hermans, ACS Catal. 2012, 2, 1108–
2
017, 52, 63–72.
[
[
18] M. Planchestainer, M. L. Contente, J. Cassidy, F. Molinari, L. Tamborini, F.
Paradisi, Green Chem. 2017, 19, 372–375.
19] a) C. Wiles, P. Watts, Green Chem. 2012, 14, 38–54; b) P. Plouffe, A.
Macchi, D. M. Roberge, Org. Process Res. Dev. 2014, 18, 1286–1294;
c) M. C. Bryan, B. Dillon, L. G. Hamann, G. J. Hughes, M. E. Kopach, E. A.
Peterson, M. Pourashraf, I. Raheem, P. Richardson, D. Richter, H. F. Sned-
don, J. Med. Chem. 2013, 56, 6007–6021.
1
117; l) S. E. Allen, R. R. Walvoord, R. Padilla-Salinas, M. C. Kozlowski,
Chem. Rev. 2013, 113, 6234–6458; m) M. Largeron, Eur. J. Org. Chem.
013, 5225–5235; n) M. Largeron, Org. Biomol. Chem. 2017, 15, 4722–
730.
2
4
Manuscript received: July 14, 2017
[3] a) A. Hacisalihoglu, A. Jongejan, J. A. Jongejan, J. A. Duine, J. Mol. Catal.
B 2000, 11, 81–88; b) N. J. Turner, Chem. Rev. 2011, 111, 4073–4087;
Version of record online: && &&, 0000
&
ChemCatChem 2017, 9, 1 – 7
www.chemcatchem.org
6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
Going with the flow: A new continu-
ous-flow biocatalytic process for the oxi-
dation of amines to aldehydes, com-
monly used as flavours and fragrances,
was achieved in an enzyme-mediated
single step. An w-transaminase from
Halomonas elongata was exploited as a
heterogeneous biocatalyst in a packed-
bed reactor, under highly favourable re-
action conditions in the presence of
pyruvate, generating l-alanine as a
benign by-product.
M. L. Contente, F. Dall’Oglio,
L. Tamborini,* F. Molinari, F. Paradisi*
&& – &&
Highly Efficient Oxidation of Amines
to Aldehydes with Flow-based
Biocatalysis
ChemCatChem 2017, 9, 1 – 7
www.chemcatchem.org
7
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ